1. Field of the Invention
The present invention relates to a wet recycling process for used impregnated active carbon by way of extraction with an organic solvent and, more particularly, to such a process to recycle TEDA (triethylenediamine) or KI (Potassium Iodide) impregnated active carbon used to adsorb radioactive organic iodide in nuclear power plants, instead of disposing of it as a radioactive solid waste material, by extracting impregnated substance and adsorbed radioactive iodide from the used impregnated active carbon with an organic solvent to regenerate active carbon, and preparing impregnated active carbon from the regenerated active carbon with TEDA or KI for use in off-gas treatment systems, thus decreasing radioactive solid waste materials and at the same time recycling raw materials.
2. Discussion of Related Art
Impregnated active carbon is a kind of active carbon used as adsorbents to enhance the adsorption efficiency for a specific toxin substance, usually hard to remove with general active carbon, or to extend the period of time of use of an adsorption column. Impregnated active carbon with its chemical activity enhanced to achieve such a use purpose is prepared from an active carbon by impregnation with special chemical compounds and adsorbed to a surface of pore wall.
As for physical adsorption, active carbon exhibits high adsorption capacity for organic iodides but the organic iodides tend to desorb in the atmosphere of high temperature and high humidity. To overcome the problem, the off-gas treatment systems in nuclear power plants use TEDA or KI impregnated active carbon.
However, impregnated active carbon is subject to deterioration so that its removal efficiency for an organic iodide is reduced as time passes. This phenomenon, termed "static ageing", is caused by oxidation or movement of sulfur, and deteriorates the activity of the impregnated active carbon. The impregnated active carbon used in normal treatment is also involved in a phenomenon called "weathering" that is it readily loses its adsorption efficiency in exposure to the external atmospheric oxygen, moisture, and organic or inorganic contaminants. When after a defined period of time, the used impregnated active carbon is revealed to be deteriorated through a performance test, it must be immediately replaced by a new one.
Impregnated active carbon will be verified for quality through the ASTM (American Standard Test Method) including a physical performance test method and a radioactive methyl iodide penetration test for impregnated active carbon, based on the ANSI N509 regulations. In association with impregnated active carbon preparation and performance test as well as the above tests and apparatus, the Korea Atomic Energy Research Institute holds the patent on a preparation method of TEDA/KI impregnated active carbon to remove radioactive iodine (KP No. 072819, Apr. 13, 1994), and it is now pending on: KP Application No. 23971 (Sept 23, 1994) for the apparatus and its operation to dry fluid phase for impregnated active carbon preparation with impregnated and dry processes facilitated; KP Application No. 23972 (Sep. 23, 1994) for the method and apparatus for impregnated active carbon performance test; KP No. 23973 (Sep. 23, 1994) for the method and apparatus for preparing radioactive methyl iodide gas for impregnated active carbon performance test; KP Application No. 14640 (Jun. 2, 1995) for the method and apparatus of extracting TEDA/KI from used impregnated active carbon; KP Application No. 14641 (Jun. 2, 1995), JP No. 2702904 (Oct. 3, 1997) and U.S. patent application Ser. No. 08/572,710 (Dec. 14, 1995) now U.S. Pat. No. 5,719093 for the method an apparatus of removing TEDA and methyl iodide from used TEDA impregnated carbon by using the fluid phase; KP Application No. 14642 (Jun. 2, 1995), JP Application No. 327609, Dec. 15, 1995), and U.S. patent application Ser. No. 08/572,700 (Dec. 14, 1995) now U.S. Pat. No. 5,792,720 for the method and apparatus of TEDA impregnated active carbon in a fluid phase adsorption column by producing TEDA vapor with hot air.
The quality of TEDA impregnated active carbon to use in the nuclear power and other common industries can be determined by a test for physical properties based on the ASTM test and an adsorption performance test using a radioactive organic iodide isotope. When the impregnated active carbon used to remove radioactive organic iodide in the off-gas treatment system of a nuclear power plant is determined from the performance test to have deteriorated adsorption efficiency, it has to be replaced by a new one. The used TEDAIKl impregnated active carbon that absorbs radioactive organic iodide is usually classified as a radioactive solid waste material and stored in a special waste storing place. As the quantity of used impregnated active carbon is increased with increasing time of nuclear power plant operation, it is required to recycle the used impregnated active carbon instead of conventional incineration or solidification disposal treatment.